I think you'll find it's around £700 million rather than the billions. The airlines actually stumped up around £50 million and borrowed the rest through NATS, hence the stupidly large debt, which has arisen from buying itself!
And as for the 'massively needed' investment, well some, infact quite a lot, went on penalty clauses paid to contractors when NATS cancelled lots of development projects. What a great deal for everyone!!!!!!